Treatment of hydrocarbons



Patented Apr. 6, 1943 TREATMENT OF HYDROCARBON S Walter A. Schulze, Ar ham H. Short, Bartl mas A. Ruoho, and Graesville, Okla, assiznors to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application June 7, 1941, Serial No. 397,135

7 Claims. (Cl. 196-28) This invention relates to a process for removing carbonyl sulfide from hydrocarbon fluids, and to a specific reagent therefor. More specifically, this invention relates to the treatment of hydrocarbons, including the so-called normally gaseous hydrocarbons,'from any source for the selective removal of carbonyl sulfide associated with said hydrocarbons.

Hydrocarbon fluids such as those obtained from crude petroleum oils and other sources usually contain varying amounts of deleterious sulfur compounds as impurities. The kinds and amounts of sulfur compounds occurring in any hydrocarbon fluid vary with the source material and with the method of manufacturing and processing said fluid. For example, thermal cracking operations have a tendency to convert hydrogen sulfide and open-chain sulfur compounds into cyclic compounds and to cause the combination of hydrogen sulfide with carbon compounds to form organic sulfur compounds including carbon sulfides.

Many of the sulfur compounds present in hydrocarbon fluids are detrimental to the processing or marketing of said fluids or of products derivable therefrom. Thus, there are conventional methods for removing hydrogen sulfide irom hydrocarbon fluids and for converting mercaptans to less obnoxious form. Further,

there are means known to'the art for extracting mercaptans as such. However, carbonyl sulfide, a sulfur compound occurring in the lowerboiling products from the thermal processing of hydrocarbon oils does not belong in the classifications mentioned, and being relatively inert is not satisfactorily removed by conventional treating processes employed by the industry for the removal of hydrogen sulfide, mercaptans, and the like.

Carbonyl sulfide is presumably formed by reaction of hydrogen sulfide with oxides of carbon under the conditions of heat and pressure and exposed metal surfaces encountered in thermal processes such as cracking and reforming operations. The pure compound has a boiling point slightly lower than that of propane, although we have found its apparent boiling point is somewhat higher in hydrocarbon mixtures. Thus, the fractionation of cracking still gases to segregate propane-butane fraction will result in the inclusion of substantially all the carbonyl sulfide present within that fraction. Likewise a butane and heavier fraction containing only minor percentages of propane may contain appreciable amounts of carbonyl sulfide.

The necessity for selectively removing carbonyl sulfide arises when a hydrocarbon fluid, e. g., a C4 fraction from refinery gases is to be substantially completely desulfurized prior to processing to efiect pohrmerization, alkylation or the like. Liquefied refinery gases containing butane and/or propane as produced for consumption as fuel have been found to contain carbonyl sulfide even after conventional methods of desulfurization; such liquefied gases are more commonly called liquefied petroleum gas or LPG. This invention provides a more complete desul furization of such hydrocarbons after conventional methods for the removal of hydrogen sulfide and mercaptans have been applied.

Carbonyl sulfide is relatively stable toward acidic reagents, and is only slowly affected -by strongly alkaline treating reagents such as so-,

lutions of caustic soda and the like. The slow reaction with alkaline reagents is apparently based on the hydrolysis of the compound to form hydrogen sulfide which reacts with the alkaline medium. In view of the relatively slow rate of the hydrolysis reaction, incomplete removal of carbonyl sulfide results in a continuous-type treating systemwherein the time of intimate contact of hydrocarbon with treating reagent is relatively short. For example, in washing a propane-butane mixture with a solution of caustic soda to remove hydrogen sulfide, we have foundthat with caustic solutions of ordinary strength,

' say 10 to 20 per cent by weight of sodium hydroxide, only 20 to 30 per cent of the carbonyl sulfide is hydrolyzed and extracted even when multi-stage contacting is employed.

We have now discovered a. method of treatment and a type of reagent which efiects the complete removal of carbonyl sulfide from hydrocarbon fluids of the type described. By the conditions of our process, a rapid reaction occurs involving the carbonyl sulfide which is converted to a. form insoluble in the hydrocarbon fluid and thus easily and completely removed from the purified fluid. The reagent we prefer to use is a solid contact type reagent comprising an adsorbent carrier impregnated with active chemical ingredients.

An object of this invention is to provide for the complete desulfurization of hydrocarbon fluids. Another object of this invention is to provide a method of removing carbonyl sulfide from hydrocarbon fluids. A further object is to provide a reagent for the removal of carbonyl sulfide from low-boiling hydrocarbon fluids. A still further object is to provide a process whereby hydrocarbon fluids which have been treated in a conventional manner for the removal of hydrogen sulfide and/or mercaptans may be freed of carbonyl sulfide remaining therein after said conventional treatment. Other objects will be apparent from the following detailed disclu sure.

We have found that while carbonyl sulfide is rather non-reactive toward acidic as well as strongly alkaline treating solutions, the reaction to form hydrogen sulfide and carbonic acid cos 21320 ms rnco. Carbonyl sulfide water hydrogen sulfide carbonic acid can be promoted by the proper conditions and brought to completion in the presence of the reagents disclosed herein. For this purpose we employ an alkaline solution and/or suspension of a cupric copper compound. The copper compound and the alkaline medium-bring about the reaction of both products of the hydrolysis of carbonylsulfide, forming copper sulfide and a salt of carbonic acid.

Solutions of soluble copper salts either inorganic or organic, suchas the chloride, acetate, sulfate, etc., are used to advantage, as well as suspensions of insoluble copper compounds such as the hydroxide, oxide, carbonate, etc. Ordinarily, except in the case of ammonia complexes, the soluble salts are converted more or less completely to the hydroxide by action of the alkaline medium. 7 r

We have found that by the use of our solidtype reagent a more complete removal of carbonyl sulfide is obtained than by the use of aqueous solutions of the reagents disclosed herein in the absence of adsorbent carriers. This client is due in part to the great amount of reagent which is exposed to the hydrocarbon fluid on the surfaces of the adsorbent carriers.

Then, too, there are no emulsion difllculties such as are encountered when aqueous alkaline solutions are mixed with hydrocarbon fluids. Of course, water must always be present on the carrier in appreciable quantities to permit the hydrolysis reaction to proceed. This essential water may be added through the use of aqueous solutions, or otherwise added to the carrier as will be hereinafter more fully shown. In some instances, the stream of hydrocarbon fluid being treated may be supplied with a small quantity of water to prevent desiccation of the solid reagent.

A further advantage of our process of treating with a solid reagent is that we may obtain long contact time of hydrocarbon with the reagent and thus promote complete removal of carbonyl sulfide. Within our preferred range of treating rates, about 0.5 to liquid volumes per hour per volume of reagent the contact time ranges from about 12 minutes to two hours. This range is in contrast to contact times of ordinarily less than three minutes in processes utilizing aqueous reagent solutions to treat hydrocarbons, and is partly responsible for the efilciency of our process.

In addition to the above-named advantages, our method of treating provides true countercurrent contact of hydrocarbons with the solid reagent. Thus, the reagent is spent in the direction of hydrocarbon flow while the section of the reagent bed adjacent to the hydrocarbon exit port is least spent and is most effective for the removal of the lowest concentrations of carbonyl sulfide.

Since the copper compounds described herein will react preferentially with hydrogen sulfide and/or mercaptans, we prefer to operate our processes to treat only hydrocarbon fluids which have undergone treatments designed to remove these types of sulfur compounds. Treatment by known methods to remove hydrogen sulfide and/or mercaptans may be given to the fluid containing carbonyl sulfide immediately prior'to passage over the reagent herein disclosed or at any time previous thereto. Or the conventional desulfurizing treatment or treatments may be made on a crude material which is subsequently fractionated to give the hydrocarbon fraction in question, or on charge stocks to conversion processes which produce the low-boiling hydrocarbons. Any suitable methods known to the art may be used for preliminary removal of hydrogen sulfide and/or mercaptans; such methods include copper sweetening, treatment with bauxite, fractionation and removal by chemicals. Of course, if hydrogen sulfide, for instance, is not present in appreciable quantities in the hydrocarbons, treatment for hydrogen sulfide removal is not necessary. In other words, any type of treatment may be relied on which will insure that the material processed for'the removal of carbonyl sulfide in accordance with this invention be essentially free from hydrogen sulfideand mercaptans. Our purpose is to avoid an uneconomic spending of our reagent which would prevent complete removal of carbonyl sulfide and add greatly to the operating costs. Hydrogen sulfide and mercaptans are ordinarily present in hydrocarbon fiuids in far greater concentrations than carbonyl sulfide and may be more economically removed by processes featuring regeneration of the treating solutions. Thus our reagent could react only with minor traces of hydrogen sulfide and/or mercaptans remaining in hydrocarbon fluids after treatment by conventional processes.

The reagent may be prepared by impregnating fullers earth or other clay-type minerals, synthetic aluminas or various adsorbent carriers with a solution of a copper salt in alkaline media. Alternately, neutral copper salt solutions may be added to the adsorbent, and converted to alkaline suspensions of the hydroxide or other basic salts by subsequent addition of a dilute alkaline solution. Copper salts form a soluble complex with ammonia, and impregnation may be accomplished with a suitable ammoniacal copper salt solution. If the excess of ammonia is later driven oil, an alkaline suspension 01' copper hydroxide will remain on the adsorbent. In some cases it may be desirable first to spray the adsorbent with a suitable alkaline solution and then to add a solid copper compound such as a copper salt or copper hydroxide in finely divided form to the stilldamp adsorbent.

It is necessary to maintain anaqueous solution phase on the surface of the adsorbent material throughout the period of use of the above described reagents. Thus the use of dry metal salts is not contemplated in our process. It is also necessary to have a pH in the adsorbed solution of above about 8 and preferably nearer 12 or above to promote the reaction of carbonyl sulfide with the reagent solution and to secure satisfactory results in the use of said reagents. The preferred range of pH in which optimum results are obtained is between about 8 and 14. The

' necessary alkalinity may be obtained by the use of alkali metal or ammonium hydroxides or in some cases with alkaline earth metal hydroxides.

The amount of copper salt to be added will depend on the solubility of the salt in the chosen alkaline medium and/or on the adsorptive capacity oi. the carrier. In general, weights of copper compound in the range of 1 to 10 per cent of the reagent weight are sufficient and avoid mechanical losses from the surface of the adsorbent material. The water content of the reagent preferably ranges from about 5 to 25 per cent, although somewhat lower concentrations may sometimes be used while the upper limit 01' water content depends to a large extent on the adsorptive capacity of the carrier.

The following examples will serve to illustrate methods of preparing and using satisfactory reagents according to our process. Numerous modifications of the reagent preparations will be obvious to those skilled in the art, and therefore are within the scope of our invention.

Ewample I Fuller's earth was impregnated with five per cent by weight of cupric acetate. Following this treatment, sufllcient dilute sodium hydroxide soivtion was added to the reagent to precipitate all of the copper salt as cupric hydroxide and result in a pH above 12 in the adsorbed aqueous phase.

A mixture of liquid propane and butane was passed over this reagent after treatment for the removal of hydrogen sulfide and mercaptans. The hydrocarbon fluid contained about 0.005 per cent by weight of carbonyl sulfide and less than 0.0001 per cent after treatment.

Our process is conveniently carried out at ordinary atmospheric temperatures between about 30 and 110 F. although slightly higher temperatures may be used if desired.

Pressures in our process are usually low superatmospheric pressures between 50 and 500 pounds gage. Operating pressures may depend upon the hydrocarbon being treated. Thus when treating butane or propane in liquid phase, sufiicient pressure is used to avoid vaporization.

It is usually desirable to treat in liquid phase, since the volume of reagent required for nominal now rates of from 0.5 to 5 volumes per hour per volume of reagent is not excessive. However,

treating the normally gaseous hydrocarbons in vapor phase is satisfactory if provision is made in the size of the reagentbed to allow contact times corresponding to linear vapor velocities of under about five feet per minute.

We claim:

l. A process for the removal of carbonyl sulfide from hydrocarbon fluids essentially free of hydrogen sulfide and mercaptans' comprising the step of contacting said hydrocarbon fluid with a solid reagent comprising an adsorbent carrier impregnated with an aqueous solution of a soluble cupric salt, the impregnating solution having a pH between the limits of approximately 8 approximately 1 to 10 between the limits 2. A process for the removal of carbonyl sulfide from hydrocarbon fluids essentially free o1 hydrogen sulfide and mercaptans comprising the step of contacting said hydrocarbon fluid with a solid reagent comprising an adsorbent carrier impregnated with an aqueous ammoniacal solution of a. soluble cupric salt to the extent of from percent of the cupric salt, the impregnating solution having a pH between the limits of. approximately 8 to 14.

3. A process for the removal of carbonyl sulfide from hydrocarbon fluids essentially free of hydrogen sulfide'and mercapt-ans comprising the step of contacting said hydrocarbon fluid with a solid reagent comprising an adsorbent carrier impregnated with an aqueous alkali solution and then treated with a cupric compound to the extent o1' from approximately 1 to 10 percent cupric compound, the aqueous alkali solution having a pH between the limits of approximately 8 to 14.

4. A process for the removal of carbonyl sulfide from hydrocarbon liquids essentially free of hydrogen sulfide and mercaptans comprising the step or contacting said hydrocarbon liquids with a solid reagent at a liquid flow rate of from approximately 0.5 to 5.0 liquid volumes per volume of reagent per hour, the solid reagent comprising an adsorbent carrier impregnated with an aqueous ammoniacal solution of a soluble cupric salt to the extent of from approximately 1 to 10 percent or the cupric salt, the impregnating solution having a pH between the limits of approximately 8 to 14.

5. A process for the removal of carbonyl sulfide from hydrocarbon liquids essentially free of hydrogensulfide and mercaptans comprising the step 01' contacting said hydrcarbon liquids with a solid reagent at a liquid flow rate of from approximately 0.5 to 5.0 liquid volumes per volume of reagent per hour, the solidreagent comprising an adsorbent carrier impregnated with an aque-' ous alkali solution and then treated with a cupric compound to the extent of from approximately 1 to 10 percent cupric compound, the aqueous alkali solution having a pH between the limits'of approximately 8 to 14.

0. A process for the removal of carbonyl sulfide from hydrocarbon vapors essentially free of hydrogen sulfide and mercaptans comprising the step of contacting said hydrocarbon vapors with a solid reagent at a linear vapor velocity of under approximately 5 feet per minute, the solid reagent comprising an adsorbent carrier impregnated with an aqueous ammoniacal solution of a cupric saltto the extent oil from approximately 1 to 10 percent cupric salt. the impregnating solution having a pH between the limits 01' approximately 7. A process for the removal of carbonyl sulfide from hydrocarbon vapors essentially free of hydrogen sulfide and mercaptans comprising the step of contacting said hydrocarbon vapors with a solid reagent at a linear vapor velocity of under approximately 5 feet per minute, the solid reagent comprising an adsorbent carrier impregnated with an aqueous alkali solution and then treated with a cupric compound to the extent of from approximately 1 to 10 percent cupric compound, the aqueous alkali solution having a pH of approximately 8 to 14.

WALTER A. SCHULZE. ARMAS A. RUOHO. GRAHAM H. SHORT. 

